Velocity modulation electron discharge device



' A ril 26, 1960 L. POLLACK ETAL VELOCITY MODULATION ELECTRON DISCHARGE DEVICE 2 Sheets-Sheet 1 Filed June 12, 1957 lnvenlors LOU/5 POLA CK HYHAIV Colo AN y 01 4c. W

' Agent April 26, 1960 1.. POLLACK A VELOCITY MODULATION ELECTRON DISCHARGE DEVICE Filed June 12, 1957 2 Sheets-Sheet 2 f/YMAN COLON/ IN By Agent of klystron However, at best,

circuitto obtain maximum VELOCITY MODULATION ELECTRON DISCHARGE DEVICE and Hyman Goldman, Great International Telephone and N.J., a corporation of Louis Pollack, Clifton,

Notch, N.J., assignors to Telegraph Corporation, Nutley, Maryland Application June 12, 1957, Serial No. 665,337 12 Claims. (Cl. 315-5.46)

velocity modulation electron discharge devices, such as klystron amplifiers and the like, fiat over a much wider' band of frequencies than have heretofore been possible.

Heretofore, the amplitude versus frequency response amplifiers has been mainly determined by the input and low level intermediate cavity resonators. These resonators operating as they do with low levels of beam velocity modulation have correspondingly little beam loading and a resulting high Q. When the simple cavity resonators are synchronously tuned, the overall response in cascade is quite narrow, and in the UHF (ultra-high frequency) range the bandwidth is less than 0.05 percent of the operating frequency. To improve this bandwidth, 7 is possible to utilize characteristics of multicavity resonator klystrons staggered tuning that is partially analogous to cascaded staggered single tuned negative grid voltage amplifiers. this alignment yields fractional bandwidths no greater than approximately 0.5 percent if power gains are to be kept at a usable level. I 7

An object of this invention is to provide a cavity resonator arrangement to increase the bandwidth capabilities of klystron amplifiers.

Another object of this invention is to provide a cavity resonator arrangement forklystron amplifiers enabling the achievement of fractional bandwidths of at least 2.5 percent in the upper UHF region with power gains of approximately 35 db.

Still another object of this invention is to provide'a double cavity resonator arrangement to provide a relatively broadband klystron amplifier.

A further object of this invention is to provide a double cavity resonator arrangement to obtain relatively wideband operation of multicavity resonator klystron amplifiers by means of resistive loading of one resonator of said double cavity resonator.

A feature of this invention is the provision of a first cavity resonator having a gap therein coaxial of an electron beam path for passage of an electron beam therethrough in coupled relation with the first resonator and a second cavity resonator remote from the beam path and in coupled relation with the first resonator to provide in conjunction therewith a double tuned circuit coupled to the electron beam to increase the bandwidth of velocity modulation amplifiers, such as klystrons.

Another feature of this invention is the provision of a first cavity resonator having a gap therein coaxial of an electron beam path for passage of an electron beam therethrough in coupled relation with the first resonator,

' a second cavity resonator remote from the beam path and resonator to provide in in coupled relation with the first conjunction therewith a double tuned circuit coupled to the electron beam and a resistive load coupled to the second cavity resonator to artificially load the double tuned frequency response of which permit a form of flatness of response and maxiin coaxial of an electron [tron beam therethrough waveguide resonator, a coaxial cavity resonator remote at Fig. 1.

from the beam path circuit comprising two 2,934,672 Patented Apr. 26, 19 60 Ice mum impedance for a specified bandwidth across the klystron interaction gap.

Still another feature of this invention is the provision of a rectangular waveguide resonator having agap therebeam path for passageof elec in coupled relation with the 'a'double tuned circuit coupled to the electron beam and aresistive load capacitively coupled to the coaxial resonator to cooperate in carrying out the objects and other features of this invention.

A further feature of this invention is the provision of a rectangular waveguide resonator having a gap therein coaxial of an electron beam path for passage of an electron beam therethrough in coupled relation with the waveguide resonator, and a coaxial cavity resonator remote and in a coupled relation with the waveguide resonator to provide in conjunction therewith a double tuned circuit coupled to the electron beam and a resistive load capacitively coupled to the coaxial resonator.

The-elements of the double tuned circuit arrangement control of waveguide cavity Q and, hence bandwidth, by varying the coefiicient of coupling of an inductive loop extending from the coaxial resonatorinto the field of the waveguide resonator enclosing the klystron interaction gap. The adjustablecoefficient of coupling may be accomplished by varying the angular position of the inductive loop withrespect to the magnetic field or the physical penetration of the inductive loop into the waveguide cavity. By making the intercavity coupling loop a part of the secondary tuned circuit, the series inductance inherent in coupling loops is utilized as part of the coaxial resonator. The resistive load coupled to the secondary tuned circuit formed by the coaxial resonator enables the artificial loading of the network to obtain the proper conditions for transitional coupling and hence transitional response. By the term transitional response or coupling, is meant the maximum coupling between the ,two cavities which will give the broadest fiat top amplitude versus frequency response. This occurs just prior to obtaining the usual double peak response condition of critical coupling.

Another feature of this invention includes coupling the input RF energy into the coaxial resonator of the double tuned circuit and loading the circuit by a' resistive load coupled to the waveguide resonator through a low inductance loop.

Another feature of this invention includes coupling the output energy at the final klystron gap to a double tuned waveguide resonators mutually coupled by an iris in the common wall thereof thereby being useful as a high power output double tuned circuit.

Still a further feature of this invention is the provision of a multicavity resonator klystron wherein each of the cavity resonators contain one or more of the above featuresto achieve a relatively broadband klystron amplifier.

The above-mentioned and other features and objects of this invention will become more apparent by'reference to the following description taken in conjunction with the accompanying drawings, in which:

Fig. 1 is a diagrammatic representation of klystron amprinciples of this invention;

Fig. 2 is an equivalent circuit diagram of the radio frequency circuit of the klystron of Fig. 1;,and

Fig. 3 is a cross-sectional view taken along line .3--:3

reference to-Fig. 1.

collector electrode 4.

interaction gaps 10 therebetween. structure and the drift tubes, as well as the collector 4,

by the first five klystron The description of the structure utilized in conjunction with a klystron amplifier to carry out the objects and features of this invention will be discussed primarily with The equivalent circuit components will be identified in Fig. 2 by the same reference charac- 'tersemployed in Fig. 1, but primed. Tlie'klystron ampli- -fi'er may consist of a filament 1 heating acathode' 2 for emission of electrons and a focusing electrode 3 for formation of the electrons into a relatively narrow electron beam for propagation along an electron beam path to Appropriate heating potential for filament 1 is supplied from source 5 through the transformer-6. Potentials for the other electrodes are supplied in a conventional manner from sources 7 and 3, as illustrated. Intermediate the beam'forming electrodes and collector electrode 4 are disposed a plurality of drift tubes 9 spaced along the beam path and provided with The beam forming would normally be closed in a vacuum enclosure 4a and the electron beam would be focused along its beam path by means of a magnetic field focusing arrangement (not shown).

The velocity modulation action which takes placeat the interaction gaps 10 and the density modulation which takes place in the drift tubes 9 are frequency-sensitive mechanisms and, therefore, the 'usual klystron with conventional high Q tuned circuits is inherently arnarrow However, by utilizing the broadband tuned circuits of this invention at the interaction gaps 10, bandwidths of from 2.5 percent of center frequency or greater can be achieved, depending on the number of cascaded cavities and power gain required.

The constructionof these double tuned circuits associated with the first five gaps of the klystron amplifier takes the form of cavity resonators 11-1111 tuned tothe operating frequency of the device, such as a rectangular waveguide cavity resonator. The klystron interaction gaps '10-10d may be considered to be a part of the resonators 11-114 arranged coaxially of the electron beam path in a manner whereby an interaction takes place between the electron beam and resonators 11-11d. The propagation mode in cavity resonators 11-11d is the principalor dominant one and the resonators 11-11d are tuned to the operating frequency by moving the primary sliding shorts 12 as illustrated in Fig. 3. To carry out band device.

the objects and features of this invention, resonators 11-11d have added thereto coaxial resonators 13-13d mutually coupled to resonators 11-11d through inductive coupling loops 14'14a'. 'The resonant frequency of resonators 13-13d is varied or tuned by moving the sliding plungers or short circuiting elements 15-15d and/or varying thesize or depth of penetration of loops 14-14d. Depth of penetration means the physical length of loops 14-1411 extending into resonators 11-11d. Adjustment of the mutual coupling between resonators 11111d and 13-13d is provided by rotating the coupling loops .by

means of rotatable center conductors 16-,16d. Resistance loading of coaxial resonators 13a, 13b, 13c and 13d of the intermediate resonant circuits 17. is provided by coupling resistive loads 18-180 to.coaxial resonators .13a.13d thereof through means of variable capacitive couplings 19-19c. Equivalent capacitieslS-lSd may be considered part of resonant coaxial circuits 13-13d. All the .above mentioned variable adjustments may be brought out as vernier controls with dial calibrations. .The adjustments or controls, described above, can bemanipulated .while the coaxial resonators are coupled orconnected to the waveguide resonators mounted on the klystron and during 'all adjustments of the klystron at any power levelsof D.C.- beam: power and input radio frequency energy that may be applied to the klystron.

As depicted in Figs. 1 and 2, the resonators aifected gaps 10-10d consist of coaxial resonators 13-13:! and rectangular waveguide resonators However, in the case to the coaxial resonator 13 by means of coaxial ll-lld. The waveguide resonators 11-11d surround the klystron gaps 10-10d for velocity modulation of the electron beam. To handle the high power level, the output circuit 20 is formed by two waveguide resonators 21 and 22 mutually coupled together by a variable iris 23 located in the common wall between the resonators 21 and 22. Resonators 2,1 and 22 may be tuned by shorting plungers substantially as shown in Fig. 3. The RF energy is removed througha coaxial line 24 to a suitable load, suchas anantenna, by means of variable capacitive coupling 25.

To achieve the desired bandwidth, each circuit is loaded with an external resistor to reduce the Q and broaden the amplitude vs. frequency response characteristic. This is illustrated schematically by resistors 18-180 which are connected across the inner and outer conductors and coupled to coaxial resonators 13a-13d, thru coupling 19-19c.

of the input circuit 26, .the waveguide resonatorll is loaded'by means of resistive load 27 mg of the resonant-circuit. The input signal iscoupled line 30 and the variablecapacitive coupling means 31. The-coupling and loading of input circuit 26-is adjusted to ob tain maximum power transfer and maximal response (equal Q in the nator 11 and secondary i The intermediate circuits flatness of primary circuit waveguide resocircuit coaxial resonator 13). 17 are loaded on one side only through thecoaxial resonator to achieve the maximum impedance acrossthe klystron gap for the given band-width. In the output circuit, waveguide resonator 21 is loaded by the klystron beam impedance across the klystron gap for the given bandwidth. In the output circuit, waveguide resonator 21 is loaded by the klystron beam impedance andwaveguide resonator 22 is loaded by the output load or'antenna impedance coupled through-thecapacitive coupling 25. The load resistors used inthe first three tuned circuits, resistors 27, 18 and 18a, may be air-cooled and the load resistors of other intermediate lcircuits, resistors 18b and 180, may be coaxial linewater oads.

To simplify the alignment of the amplifier, the six Idouble tuned circuits are synchronously aligned and cenadjusted for transitional coupling with the klystron unenerg1zed. A sweep signal generator is coupled to one circuit at a time and a response observed at a test point incorporated in the circuit. Then under normal drive and power input conditions, a slight readjustment of the clrcuitwlll result in a desired response.

[The circuit described in connection with Figsjl and 2 -providesfor an external controlofintercavity coupling,

hence cavity Q, hence bandwidth, by varying the coefiimade part of. the secondarytuned circuit thereby utilizing the series inductance inherent in the coupling loop. ln

. this manner, it is possible to artificially load the network to obtain the conditions for transitional response.

thebeam. -In additiomthe'bandnarriwing characteristics considerably reduced when utilizing double tuned circuits.

invention in connection with specific apparatus,

, While we have described, above the principles of our it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims. j

Weclaim; a 1. A broadband velocity modulation electron discharge device comprising means to project an electron beam along a given path; a double tuned circuit disposed in energy exchanging relationship with said electron beam including a first cavity resonator having a gap therein coaxial of said beam path for passage of said electron beam therethrough in energy exchanging relationship with said first resonator, a second cavity resonator spaced radially from said beam path and having its outer wall integral with the outer wall of said first resonator, inductive coupling means for energy exchange between said first and second resonators and means included in each of said first and second resonators to tune each of said resonators independent of one another; and a resistor coupled to said first resonator, said resistor and said double tuned circuit cooperating to increase the effective bandwidth of said discharge device.

2. A broadband velocity modulation electron discharge device comprising means to, project an electron beam along a given path; a double tuned circuit disposed in energy exchanging relationship with said electron beam including a first cavity resonator having a gap therein coaxial of said beam path for passage of said electron beam, therethrough in energy exchanging relationship with said first resonator, a second cavity resonator spaced radially from said beam path and having its outer wall integral with the outer wall of said first resonator, inductive coupling means for energy exchange between said first and second resonators, and means includedin each of said first and second resonators to tune each of said resonators independent of one another; a means to couple radio frequency energy directly into. said second resonator independent of said first resonator; and a resistor coupled to said first resonator; said resistor and said double tuned circuit cooperating to increase the efiective bandwidth of said discharge device.

3. A broadband velocity modulation electron discharge device comprising means to project an electron beam along a given path; and a double tuned circuit to increase the elfective bandwidth of said discharge device disposed in energy exchanging relationshipwith said electron beam including a rectangular waveguide resonator having a gap therein coaxial of said beam path for passage of siad electron beamtherethrough. n, energy exchanging relationship with said waveguide resonator, a coaxial cavity resonator spaced radially from saidbeam path, the outer conductor of said coaxial resonator and the wall of said waveguide resonator being integral, means included in each of said waveguide and coaxial resonators to tune each of said resonators independent of one another, an inductive coupling loop extending from the center conductor of said coaxial resonator for energy exchange between said waveguide and coaxial resonators, and means to adjust the physical position of said coupling loop to adjust the coeflicient of coupling between said waveguide and coaxial resonators.

I 4. A broadband velocity modulation electron discharge device comprising means to project an electron beam along a given path; and a double tuned circuit to increase the eftectivebandwidth of said discharge device disposed in energy exchanging relationship with said electron beam including a first cavity resonator having a gap therein coaxial of said beam path for passage of said electron beam therethrough in energy exchanging relationship with said first resonator, asecond cavity resonator spaced radially from said beam path and having its outer wall integral with the outer wall of said' firstresonator, means included in each of said first and second resonators to tune .inductive'coupling loop for-energy exchange between along a given path;

each of said resonators independent of one another, sai

first and second resonators, and means to adjust the physical position of said coupling loop to adjust the coefficient of coupling between said first and second resonators; a resistor; and means to adjustably couple said resistor directly to said second resonator independently of said first resonator to cooperate with said double tuned circuit to increase the effective bandwidth of said discharge device.

5. A broadband velocity modulation electron discharge device comprising means to project an electron beam a double tuned circuit disposed in energy exchanging relationship with said electron beam including a. first cavity resonator having a gap therein coaxial of said beam path for passage of said electron beam therethr ough in energy exchanging relationship with said first resonator, a second cavity resonator spaced radially from said beam path and having its outer wall integral with the outer wall of said first resonator, means included in each of said first and second resonators to tune each of said resonators independent of one another, an inductive coupling loop for energy exchange between said first and second resonators, said coupling loop forming a component of said second resonator, and means to adjust the physical position of said coupling loop to adjust the coefficient of coupling between said first and secnd cavities; a resistor; and means to adjustably couple said resistor to said first resonator, said resistor and said double tuned circuit cooperating to increase the efiective bandwidth of said discharge device.

, 6. A broadbandvelocity modulation electron discharge device comprising means to project an electron beam along a given path; a double tuned circuit disposed in energy exchangingrelationship with said electron beam includinga firstcavity resonator having a gap therein coaxial of said beam path for passage of said electron beam there through in energy exchanging relationship with said first resonator, a second cavity resonator'spaced radially from said beam path and having its outer wall integral with the outer wall of said first resonator, means included in each of said first and second resonators to tune each of said resonators independent of one another, an inductive coupling loop for energy exchange between said first and second resonators, said coupling loop forming a component of said second resonator, and means to adjust the physical position of said coupling loop to adjust the coeflicient of coupling between said first and second cavities; adjustable means to couple radio frequency energy directly into said second resonator independently of said first resonator; a resistor; and means to adjustably couple said resistor to said first resonator, said resistor and said double tuned circuit cooperating to increase the effective bandwidth of said discharge device;

7. A broadband velocity modulation electron discharge device comprising means to project an electron beam along a given path; a double tuned circuit disposed in energy exchanging relationship with said electron beam including a rectangular waveguide resonator having a gap therein coaxial of said beam path for passage of said electron beam therethrough in energy exchanging relationship with said waveguide resonator, a coaxial cavity resonator spaced radially from said beam path, the outer conductor of said coaxial resonator being integral with the wall of said waveguide resonator, means included in each of said waveguide and coaxial resonators to tune each of said resonators independent of one another, an inductive coupling loop extending from the inner conductor of said coaxial resonator for energy exchange between'saidrwaveguide-and coaxial resonators, means to adjust the physical position of saidcoupling'loop to adjust the coefficient of coupling between said coaxial and waveguide resonators;

a resistor; an adjustableinductive loop coupling said resisto increase the ettective bandwidth of said discharge device; conductive means spaced from the center conductor of said coaxial resonator t capacitively couple radio frequency energy directly into said coaxial resonator independently of said waveguide resonator; and means to adjust the spacing between said conductive means and the center conductor of said coaxial resonator to adjust the amount of energy coupled into said coaxial resonator.

8. A broadband velocity modulation electron discharge device comprising means to project an electron beam along a given path; a double tuned circuit disposed in energy exchanging relationship with said electron beam including a rectangular waveguide resonator having a gap therein coaxial of said beam path for passage of said electron beam therethrough in energy exchanging relationship with said waveguide resonator, a coaxial cavity resonator spaced radially from said beam path, the outer conductor of said coaxial resonator and the wall of said waveguide resonator being integral, means included in each of said waveguide and coaxial resonatorsto tune each of said resonators independent of one another, aninductive coupling loop extending from the center conductor of said coaxial resonator for energy exchange between said waveguide and coaxial resonators, and means to'adjust the physical location of said coupling looptto adjust the coetficient of coupling between said waveguide and coaxial resonators; a resistor; conductive means coupled to said resistor and spaced from the center conductor of said coaxial resonator to capacitively couple said resistor directly to said coaxial resonator independently of said waveguide resonator; and means coupled to said conductive means to adjust the spacing between said conductivemeans and the center conductor of said coaxial resonatorto control the amount of resistance placedacross said coaxial resonator; said resistor and said double tuned circuit cooperating to increase the efiective bandwidth of said discharge device. 7

9. A broadband velocity modulation electron discharge device comprising an electron beam forming means to project an electron beam along a given path; a radio frequency input circuit disposed adjacent said beam forming means including a double tuned circuitdisposed in energy exchanging relationship with said electron beam having a first cavity resonator including a gap therein coaxial of said beam path for passage of said electron beam therethrough in energy exchanging relationship with said first resonatona second cavity resonator spaced radially from said beam path and having its outer wall integral with the outer wall of said first resonator, inductive coupling means for energy exchange between said first'and second resonators, means included in each of said first and second resonators to tune each of said resonators independent of one another, a resistor, means coupling said resistor. to said first resonator and means to couple radio frequency energy directly into said second resonator independently of said first resonator; a radio frequency output circuit disposed remote from said beamrforming means including a double tuned circuit having a first cavity resonator including a gap therein coaxial of said beam path for passage of said electron beam therethrough in energy exchanging relationship with said first resonator, a second cavity resonator spaced radially from said beam path and having its outer wall integral with the outer wall of said first resonator, inductive coupling means for energy exchange between said first and second resonators, means included in each of said first and second resonators to tune each of said resonators independent of one another, and means to couple radio frequency energy directly from said second resonator independently of said first resonator; and a plurality of intermediate double tuned circuit elements disposed intermediate said input and output circuits in energy exchanging relationship. with said electron beam, each of said intermediate circuit elements including a first cavity resonator having a gap therein coaxial of said beam path for passage therethrough in energy exchanging relationship with said first resonator, a second cavity resonator spaced radially from said beam path and having its outer wall integral with the outer wall of said first resonator, inductive coupling means for energy exchange between said first and second resonators, means included in each of said first and second resonators to tune each of said resonators independent of one another, a resistor, and means coupling said r'esistordirectly tosaid second resonator independently of said first resonator.

10. A broadband velocity modulation electron discharge device comprising an electron beam forming means to project an electron beam along a given path; a radio frequency input circuit disposed adjacent said beam forming means including a double tuned circuit disposed in energy exchanging relationship with said electron beam having a rectangular waveguide resonator including a gap therein coaxial of said beam path for passage of said electron beam therethrough in energy exchangng relationship with said waveguide resonator, a coaxial resonator spaced radially from said beam path and having the outer conductor thereof integral with the wall of said waveguide resonator, an inductive coupling loop extending from the center conductor of said coaxial resonator for energy exchange between said first and second resonators, means included in each of said waveguide and coaxial resonators to tune each of said resonators independent of one another, means to adjust the physical position of said coupling loop to adjust the coefiicient of coupling between said waveguide and coaxial resonators, a resistor, means capacitively coupling said resistor to said waveguide resonator and means to capacitively couple radio frequency energy directly into said coaxial resonator independently of said waveguide resonator; a radio frequency output circuit disposed remote from said beam forming means including a double tuned circuit having a first waveguide resonator including a gap therein coaxial of said beam path for passage of said electron beam therethrough in .energy exchanging relationship with said first resonator, a second waveguide resonator spaced radially from said beam path and having its outer wall integral with the outer wall of said first resonator, inductive coupling means for energy. exchange between saidfirst and second resonators, means included in each of said first and second resonators to tune each of said resonators independent of one another, and means to capacitively couple radio frequency energy directly from said second resonator independently of said first resonator; and a plurality of intermediate dour ble tuned circuit elements disposed intermediate said input and output crcuits in energy exchanging relationship with said electron beam, each of said intermediate circuit elements including a waveguide resonator having a gap therein coaxial of said beam path for passage there through in energy exchanging relationship with said waveguide resonator, a coaxial resonator spaced radially from said beam path and having the outer conductor thereof integral with the wall of said waveguide resonator, an inductive coupling loop extending from the center conductor of said coaxial resonator for energy exchange between said first and second resonators, means included ineach of said waveguide and coaxial resonators to time each of said resonators independent of one another, a resistor, and means capacitively coupling said resistor directly to said coaxial resonator independently of said waveguide resonator.

11. A broadband velocity modulation electron dis charge device comprising means to project an electron beam along a given path; and a double tuned circuit to increase the effective bandwidth of said discharge device disposed in energy exchanging relationship with'said electron beam including a first cavity resonator having a gap therein coaxial of said beam path for passage of said electron beam therethrough in energy exchanging relationship with saidfirst resonator, a second cavity resonator spaced radially from said beam path and having its outer wall integral with the outer wall of said first included in said waveguide resonator to tune said waveresonator, means included in said first resonator to tune guide resonator independent of said coaxial resonator, an said first resonator independent of said second resonator, inductive coupling loop extending from the center conan inductive coupling loop for energy exchange between ductor of sa1d coax1a1 resonator for energy exchange said first and second resonators, a tuning arrangement 5 between said waveguide and coaxial resonators, a tuning for said second resonator including a first means in sa1d arrangement for said coaxial resonator including a first second resonator and a second means to adjust the penemeans in said coaxial resonator and a second means to tration of said coupling loop into said first resonator coadJust the penetration of sa1d coupling loop lnto sa1d 7 operating to tune said second resonator, and means to waveguide resonator cooperating to tune sa1d coaxial resoadjust the angular position of said coupling loop within 10 means to adjust the angular Position of Said said first resonator to adjust the coefficient of coupling coupling loop within said waveguide resonator to adjust between said first and second resonators. the coefficient of coupling between said waveguide and 12. A broadband velocity modulation electron disa i reso tors.

charge device comprising means to project an electron beam along a given path; and a double tuned circuit to 15 References Cited in the file of this patent increasethe effective bandwidth of said discharge device UNITED STATES PATENTS disposed in energy exchanging relationship with said Re 23 284 McArthm. et a1 Oct 17 1950 electron beam including a rectangular waveguide reso- 2,256,824 Hansen et 1942 nator having a gap therein coaxial of said beam path 2,234,405 McArthur May 1942 for passage of said electron beam therethrough in energy 20 2,44 572 n A 10, 1943 exchanging relationship with said waveguide resonator, 2,55 ,97 Pierce June 12, 1951 a coaxial cavity resonator spaced radially from said beam 2,610,307 Hansen et a1. Sept. 9, 1952 path, the outer conductor of said coaxial resonator and 2,789,250 Varian et a1. Apr. 16, 1957 the wall of said waveguide resonator being integral, means 2,790,928 Reed Apr. 30, 1957 

